ABSTRACT
Theoretical calculations are presented on a new hypothetical 3,4-connected carbon net (called squaroglitter) incorporating 1,4 cyclohexadiene units. The structure has tetragonal space group P4/mmm (No. 123) symmetry. The optimized geometry shows normal distances, except for some elongated bonds in the cyclobutane ring substructures in the network. Squaroglitter has an indirect bandgap of about 1.0 eV. The hypothetical lattice, whose density is close to graphite, is more stable than other 3,4-connected carbon nets. A relationship to a (4,4)nanotube is explored, as is a potential threading of the lattice with metal needles.
ABSTRACT
The structures and electronic properties of a number of real and hypothetical ABX(2) compounds sharing (or evolving from) a single P4/mmm structural type are examined. These include the known CaCuO(2) and SrFeO(2) phases. A number of variations of this P4/mmm ABX(2) framework, some obvious, some exotic, all with a chemical motivation, were investigated: A = alkali metal, alkaline earth metal or La, B = Ti, Fe, Cu, or Pt, and X = C, O, S, C(2), H(2), or F. Careful attention was given to the d-orbital splitting patterns and magnetic states (ferromagnetic or antiferromagnetic) of these compounds, as well as their stability gauged by phonon dispersions and energetics. The most interesting as yet unmade compounds that emerged were (a) a carbide SrFe(C(2))(2), containing C(2) units with a C-C distance of 1.267 A, (b) an AeTiO(2) series, with Ti-Ti bonding, part sigma, part pi, tuned by the Ae(2+) cation size, and (c) NaPtF(2), for which a second structure was found, containing a hexagonal layering of (PtF(2))(-) molecules.
ABSTRACT
A previous report has described the crystal structure of glitter, which is a dense 3-,4-connected net composed of ethylenic columns that run parallel to the c-axis of the unit cell. Such a structure invites speculation as to its relative stiffness along that axis. A semiempirical expression due to Cohen was used in a previous communication to estimate its zero-pressure bulk modulus. This estimate exceeds that of any known material at 440 GPa. Further, by treating the ethylenic units as harmonic springs, a correction was computed for the elastic deformation of the carbon-carbon double bonds along the c-axis. This correction is on the order of 300 GPa for deformations of the double bonds of approximately 0.1 angstroms. The present communication treats the ethylenic units along the c-axis of glitter as anharmonic springs obeying a Morse potential and a Morse's law force. Within the anharmonic approximation, at modest bond length deformations, x', the bulk modulus at pressure of the glitter lattice exceeds 1 TPa.
